Introduction

Electromagnetic fields are produced by differences in voltage (electric field) or by electric current flow (magnetic field). A higher voltage difference or electric current leads to greater electromagnetic fields. Everyone is exposed to a complex mixture of weak electromagnetic fields in their living and working environment. Most of the workplaces, such as office environments, have only low electromagnetic fields that can be regarded as harmless. On the other hand, in some work environments there are higher EMFs that need to be taken into account. For example, occupational activities that can result to higher EMF exposure are electric welding, glue drying, certain medical imaging devices, RF (radio frequency) sealing, induction heating and electrolysis processes. In addition there are also synergistic effects due to simultaneous exposure to various biological, chemical, and physical agents that need to be considered. These types of workplaces should conduct an exposure assessment to ascertain that the workers’ exposure is below the recommended limits. In very high overexposure situations, individuals can experience acute health effects, such as nerve stimulations at low frequencies or thermal effects at higher frequencies. The risks and exposure in the workplace can be reduced by appropriate technical measures.

Describes the number of oscillations or cycles per second in electromagnetic field (expressed in hertz (HZ).

Static fields

Fields that do not vary over time. A direct electric current will create a static magnetic field and a static electric field is created by electrical charges that are fixed in space. The earth's magnetic field is a static field.

Magnetic fields (MF)

Fields that arise from the motion of electric charges. The strength of the magnetic field is measured in amperes per meter (A/m) or in flux density (in microtesla, µT). A magnetic field is only produced when current flows. A higher current produces a greater magnetic field.

Electric fields (EF)

Exist whenever a positive or negative electrical charge is present. They exert forces on other charges within the field. The strength of the electric field is measured in volts per metre (V/m).

Power density (S)

A quantity used for very high frequencies where the depth of penetration in the body is low. It is the radiant power incident perpendicular to a surface, divided by the area of the surface. It is expressed in watts per square meter (W/m2).

Limb current (IL)

A current in the limbs of an individual exposed to electromagnetic fields in the frequency range from 10 MHz to 110 MHz as a result of contact with an object in an electromagnetic field or the flow of capacitive currents induced in the exposed body. It is expressed in ampere (A).

Extremely low frequency (ELF) fields

Frequencies up to 300 Hz.

Intermediated frequency (IF) fields

Frequencies from 300 Hz to 10 MHz.

Radio frequency (RF) fields

Frequencies of 10 MHz to 300 GHz.

Specific absorption rate (SAR)

The rate at which energy is absorbed per unit mass of body tissue. It is expressed in watts per kilogram (W/kg). Whole-body SAR is a widely accepted quantity for relating adverse thermal effects to radio frequency (RF) exposure.

Exposure limits

Workers exposure characteristics (strength of exposure and interaction with the body) to EMF’s are significantly different from that of the general public, since they will be exposed to higher levels for longer periods of time, will be considerably closer to the source, and the modulation (frequency composition) of EMF will be more complex.

In order to establish minimum EMF safety standards common across the EU, the first EMF Directive (Directive 2004/40/EC), dealing with health and safety at work was adopted in 2004. In 2013 the new EMF Directive (Directive 2013/35/EU)[1] was adopted, repealing the previous one. The directive addresses the protection of workers exposed to electromagnetic fields and the carrying out of effective and efficient risk assessments, proportional to the situation encountered at the workplace. Within the EU Directive, there are defined exposure limit values (ELV) and action levels (AL)[1] Council of the European Union, Proposal for a Directive of the European Parliament and of the Council on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields), (XXth individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC), Brussels, 21 September 2012.</ref>. The action levels are directly measureable, physical quantities established for the purpose of simplifying the process of demonstrating compliance with the relevant exposure limit values. Exposure limit values are based on scientifically well-established, short term and acute, direct effects (such as thermal effects and electrical stimulation of tissues).

Both exposure limit values and action levels are frequency dependent and consist of two levels.

The first level corresponds to the levels of exposure above which workers might be subject to transient disturbances in sensory perception and minor changes in brain function (sensory effects ELV).

The second level corresponds to the levels of exposure above which workers might be subject to adverse health effects, such as thermal heating or stimulation of nerve and muscle tissue (health effects ELV).

In practice almost invariably only the action limits are used when conducting a risk or exposure assessment. The exposure limit values represent the limits for electric fields induced in the body from exposure to time varying electric and magnetic fields and therefore are not practicable in everyday risk analysis. An assessment against exposure limit values is usually done when there are no other alternatives (one example would be a case where a very localised source was situated at a distance of only a few centimetres from the body [2]).

Exposure limit values for static magnetic fields

Exposure limit values for external magnetic flux density are defined in the frequency range of 0 to 1 Hz (Table 2). These limit values are based on the recommendation of the International Commission on Non-Ionizing Radiation (ICNIRP) [2][3] and set out in the annex II of the article of the directive. [1]

Source: Adapted from recommendations of ICNIRP and set out in the annex II of the EMF directive. [1][2][3]

Action levels for electric and magnetic fields and power densities

Action levels correspond to calculated or measured electric and magnetic field values in the workplace in the absence of the worker. With respect to electric fields, the Low and High AL’s are levels which relate to the specific protection or prevention of the effects specified in Directive. With respect to magnetic fields, the AL’s are levels which relate to the sensory effect’s ELV and to the health effect’s ELV. In the Table 3 ALs for some common frequencies and sources in the working environments are presented. Complete frequency dependent AL’s are detailed in the European Directive [1]

Table 3: Examples of EMF sources and the respective ALs in the work environment

With respect to the non-thermal effects (0 Hz- 10MHz), the action levels are Root-mean-Square values which are equal to peak values divided by √2 for the sinusoidal field. In the work environment usually the electromagnetic fields encountered are non-sinusoidal (e.g. certain electric welding processes) and the frequency content needs to be taken into account. The exposure evaluation should be based on the weighted peak method [4] or some other scientifically proven method leading to approximately equivalent and comparable results.

For the thermal effects (100 kHz – 300 GHz), the action levels are to be averaged over 6 min period. For RF pulses, the peak power density averaged over the pulse width must not exceed 1000 times the respective power density AL value. For multi-frequency fields the analysis is based on summation.

Impact on health

Everyone is exposed to a complex mixture of weak electric and magnetic fields, both at home and at work, from the generation and transmission of electricity, domestic appliances and industrial equipment, as well as from telecommunications and broadcasting. Tiny electrical currents exist in the human body due to the chemical reactions that occur as part of many normal bodily functions, even in the absence of external electric fields [5].

Changes in our environment or external stimuli may evoke biological effects. These effects are part of normal life and the body can adjust to most of these situations. Biological effects themselves are not dangerous to health. However, in some cases, when the stimulus is very strong or long lasting, the effects can lead to adverse health effects. The way that the electromagnetic fields can affect health will depend on the frequency, strength and duration of the exposure. The occupational exposure limits are set in such a way that there will be no adverse health effects as long as there is adherence to the limits.

Health effects at low frequency fields

With low frequency fields (<100 kHz), the main biological effect is the stimulation of the nervous system and subsequent sensory effects. Very strong electromagnetic fields can induce internal electric fields that stimulate nerves and muscles. The induced electric fields may disrupt the activity of nerves and these can trigger, for example, visual magnetophosphenes (flashes of light seen when one is subjected to a changing magnetic field such as when in an MRI). However, there is no evidence that the magnetophosphenes have any adverse health effects. Nonetheless, continuous visual disturbances are annoying and may lead to other secondary risks in the workplace. Very strong static magnetic fields (above 2 T) can also produce nausea and vertigo due to static field gradients [6]. The effects at low frequencies are acute and will cease when the source is removed. The Intermediated frequency (IF) fields between 300 Hz and 10 MHz have been less extensively studied. Well-known biological effects are nerve stimulation at low frequencies and heating at high frequencies. These effects are obtained by extrapolation from ELF and RF field mechanisms. Occupational exposure to IF fields in certain areas is higher than the exposure of the general public. However, there is a paucity of research on IF and health risks in occupational settings or for the general public are scarce.

Health effects from radio frequency (RF) fields

With respect to radio frequency fields the tissue heating is the principal mechanism. Tissue heating is the most widely accepted mechanism of interaction between RF energy and the human body. The effects can result from elevations of tissue temperature induced by RF energy deposited on or absorbed by biological systems through local, partial-body or whole-body exposures [7]. Short exposure durations may not be sufficient to significantly contribute to tissue temperature rise. In this case, the time rate of rise in temperature is proportional to SAR (specific adsorption rate). With longer exposure durations the rise in temperature depends on the tissue, thermal regulatory behaviour and an active compensation mechanism. Under normal conditions, a temperature rise of the order of 1°C can result from an SAR input of 4 W/kg. It should be noted that this temperature rise is within the normal range of human thermoregulatory capacity. However, if there is human contact with metallic objects in the high-frequency EMF field, then this can lead to shocks and burns as adverse indirect effects.

Clapp and colleagues described new evidence in a 2007 literature study on environmental and occupational causes of cancer. Despite weaknesses in some individual studies, they concluded that recent publications had strengthened the evidence linking specific exposure with increased risk of cancer, among them brain cancer from exposure to nonionizing radiation, particularly radiofrequency fields emitted by mobile telephones [8]. In 2011 the International Agency for Research on Cancer (IARC) has classified the radiofrequency fields (RF) as Group 2B in the IARC scale of carcinogenic risk to humans. The 2B category is used for agents for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals. It may also be used when there is inadequate evidence of carcinogenicity in humans but there is sufficient evidence of carcinogenicity in experimental animals; meaning a positive association has been observed between exposure to the agent and cancer for which a causal interpretation is considered by the Working Group to be credible, but chance, bias or confounding could not be ruled out with reasonable confidence.[9]

Risk assessment

In the workplace, all the risks arising from the electromagnetic fields must be assessed. If needed, the electromagnetic fields to which the workers are being exposed should be measured or calculated. Existing information can be used when undertaking the assessment. For example, this information can be relevant standards[10], national guidelines, exposure databases and information provided by the equipment manufacturer.

The exposure assessment by measurement or calculations is needed if the risk assessment cannot be achieved only by the available information. The results of measurements or calculations are compared with ELV’s to determine the possible risk to workers. During the risk assessments, the following issues [1] need to be taken into account:

the frequency, the level, duration and type of exposure, including distribution over the worker’s body and the space of workplace;

any direct biophysical effects in the human body directly provoked by the presence in electromagnetic field;

any effects concerning the health and safety of workers at particular risk, in particular workers who wear an active or passive implanted medical device (such as cardiac pacemakers), workers who wear body worn medical devices (such as insulin pumps), and pregnant workers;

any indirect effects on an object, due to its presence in the electromagnetic field, which may become the cause of a safety or health hazard;

the existence of replacement equipment designed to reduce the level of exposure to electromagnetic fields;

appropriate information obtained from health surveillance;

information provided by the manufacturer of equipment and other relevant available health and safety related information;

multiple sources of exposure;

simultaneous exposure to multiple frequency fields.

The risk assessment must be kept in a safe and updated when necessary. The risk assessment may also include a justification to explain why a further risk assessment is unnecessary.

Workers at particular risk

Under certain circumstances, the EMF can pose an additional risk to specific workers. For example, these workers at particular risk are:

In these cases, the employer should perform a specific risk assessment such that the individual conditions are taken into account. Risk assessment guidance for cardiac pacemakers users in the workplace have been published, for example by the European Committee for Electrotechnical Standardization and Finnish Institute of Occupational Health[11], [12], [13]. The risk assessments in these documents are based on the approach that, according to EN 45502-2-1 [14], pacemakers are expected to work uninfluenced as long as the General Public Reference levels of Council Recommendation 1999/519/EC [15] are not exceeded (except for static magnetic fields and for pulsed high frequency electromagnetic fields).

Mitigation and prevention

Due to the nature of electromagnetic fields, there is very little advantage to be gained in using personal protecting equipment (PPE) to reduce the exposure. Certain PPE are needed and useful to protect the worker from the physical risks related to EMF. For example, these risks are the optical radiation and flying objects emitted from electric welding processes.

The most effective way to reduce the EMF exposure is to control it at its source. There are several approaches that can be used for prevention and mitigation of exposure[16][1]. For example, the following means can be applied at the workplace:

the design and layout of workplaces and workstations;

appropriate delimitation and access measures (e.g. floor markings, fences) in order to limit or control access;

technical measures to reduce the emission of electromagnetic fields, including, where necessary, the use of interlocks, shielding or similar health protection mechanisms;

adopting other working methods that entail less exposure to electromagnetic fields;

the choice of equipment emitting less electromagnetic fields, taking account of the work to be done;

in the case of exposure to electric fields, measures and procedures to manage spark discharges and contact currents via technical means and the training of workers;

appropriate maintenance programmes for work equipment, workplaces and workstation systems;

limitation of the duration and intensity of the exposure.

The European EMF Directive stipulates that appropriate health surveillance shall be carried out and health records and their availability shall be provided for in accordance with national law and/or practice. The results of health surveillance shall be preserved in a suitable form that allows them to be consulted at a later date, Individual workers shall, at their request, have access to their own personal health records. If any undesired or unexpected health effect is reported by a worker, or in any event where exposure above the ELVs is detected, the employer shall ensure that appropriate medical examinations or individual health surveillance is provided to the worker(s) concerned, in accordance with national law and practice.[1]

In order to facilitate the implementation of the Directive the European Commission shall make available non-binding practical guides at the latest six months before 1 July 2016.[1] Public Health England (PHE) was awarded the contract to develop this guide and it is expected to be published in January 2016.[17]

References

↑ 1.001.011.021.031.041.051.061.071.081.091.10 European Parliament and Council, 'Directive 2013/35/EU of 26 June 2013 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields) (20th individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC) and repealing Directive 2004/40/EC', Official Journal of the European Union L 179/1, Brussels, 29 June 2013. Available at: [1]

↑ 'Council Recommendation of 12 July 1999 on the limitation of exposure of the general public to electromagnetic fields (0 Hz to 300 GHz)', 1999/519/EC, Official Journal of the European Communities L199/59. Available at: [9]

↑ CENELEC – European Committee for Electrotechnical Standardization, Safety of machinery. Assessment and reduction of risks arising from radiation emitted by machinery. Part 1: General principles, -EN 12198-1:2009, 2009.